1. Field of the Invention
The present invention relates to a rigid endoscope with hermetic seal. More particularly, the present invention relates to a rigid endoscope of which a hermetic shell in a rigid tube can be sealed reliably with a simple structure.
2. Description Related to the Prior Art
A rigid electronic endoscope includes a rigid tube or endoscope tube and a grip handle. The rigid tube is used for entry in a body cavity of a patient. The grip handle is disposed at a proximal end of the rigid tube. The grip handle is connected to a light source apparatus for supply of light and to a processing apparatus for forming an image of an object. The rigid tube has a tip device. Window components (window plates) are provided in the tip device, including lighting window components and a viewing window component. The lighting window components apply light to the object. The viewing window component receives image light from the object. A light guide device as a fiber bundle constituted by bundling plural optical fibers has an exit end, which is opposed to the lighting window components. An imaging module is disposed behind the viewing window component, and includes a lens system for focusing and an image sensor. The light guide device extends from the rigid tube to the grip handle, and guides light from the light source apparatus to the lighting window components. The lens system focuses image light from an object in the body cavity on the image sensor upon receiving the image light through the viewing window component. The image sensor generates the image of the object and outputs an image signal. The processing apparatus forms a video image according to the image signal from the image sensor, and causes a display panel to display the image.
The rigid endoscope after use is sterilized for the purpose of preventing infection due to repeated use. An example of the sterilization is autoclave sterilization by use of saturated water vapor at high temperature and high pressure. JP-A 7-039515 discloses the rigid endoscope with suitable firmness with resistance in the presence of the saturated water vapor at high temperature and high pressure.
In the rigid endoscope of JP-A 7-039515, the lens system (objective lens) is kept positioned on a lens holder with seal packing. The image sensor (CCD) is attached to a holder positioned at the rear end of the lens holder. Resin encapsulant is provided on the surface of the lens holder and the holder, to seal the imaging module air-tightly to prevent entry of the saturated water vapor at high temperature and high pressure.
A method of sealing the imaging module is the use of the encapsulant in JP-A 7-039515. In addition, other methods of the sealing are available, for example, the imaging module is contained in a distal portion of a stainless hermetic shell of a cylindrical shape, and a sealed terminal device seals a proximal end of the hermetic shell.
In FIGS. 9A and 9B, a structure of sealing a proximal end of the hermetic shell is illustrated. An endoscope has an imaging module (not shown), a hermetic shell 201 (case or container), and a sealed terminal device 200 or lead-through device (sealing closure device). The hermetic shell 201 contains the imaging module. The sealed terminal device 200 is attached to a proximal end of the hermetic shell 201. The sealed terminal device 200 encloses the hermetic shell 201 hermetically, and also operates to wiring of connecting lines (not shown) from the imaging module to the outside of the hermetic shell 201 in a sealed state. The sealed terminal device 200 includes an outer ring 202 or outer frame, insulating encapsulant 203, and lead-through conductors 204 (terminal pins). The insulating encapsulant 203 is disposed in the outer ring 202. The lead-through conductors 204 are set through the insulating encapsulant 203, and encapsulated with the insulating encapsulant 203 for electrical conduction from the imaging module to the outside of the hermetic shell 201.
A receiving opening 205 or inner wall (female type) is formed in a proximal end of the hermetic shell 201. A plug head 206 (male type) is defined with the sealed terminal device 200. The plug head 206 is fitted in the receiving opening 205 in a male/female coupling arrangement, to combine the sealed terminal device 200 with the proximal end of the hermetic shell 201.
The receiving opening 205 is cylindrical like the hermetic shell 201, and contains the plug head 206. The receiving opening 205 includes an inner surface 207 and a first edge surface 208. The inner surface 207 extends in the axial direction of the plug head 206 relative to the receiving opening 205. The first edge surface 208 is an end surface of the hermetic shell 201 perpendicular to the inner surface 207. Also, the plug head 206 is cylindrical and entered in the receiving opening 205. The plug head 206 includes an outer surface 209 and a second edge surface 210. The outer surface 209 extends in the axial direction, and is opposed to the inner surface 207. The second edge surface 210 is erect from the outer surface 209, and contacted by the first edge surface 208. The second edge surface 210 is a shoulder portion around the outer surface 209, and regulates an entry amount of the plug head 206 into the receiving opening 205 by contacting the first edge surface 208. An outer diameter Φ1 of the outer surface 209 is set finely smaller than an inner diameter Φ2 of the inner surface 207 for the purpose of smoothing entry of the plug head 206 into the receiving opening 205.
For fitting the plug head 206 in the receiving opening 205, the plug head 206 is pushed into the receiving opening 205 in the axial direction while the outer surface 209 is guided by the inner surface 207 of the receiving opening 205 until the first edge surface 208 comes in contact with the second edge surface 210 in FIG. 9B. As the outer diameter Φ1 of the outer surface 209 is finely smaller than the inner diameter Φ2 of the inner surface 207, there occurs a small clearance between the inner and outer surfaces 207 and 209. In view of this, the inner and outer surfaces 207 and 209 are welded together by laser welding at a weld area WP0 and a dotted circle near to the first and second edge surfaces 208 and 210 after fitting the plug head 206 in the receiving opening 205. Thus, the hermetic shell 201 can be closed air-tightly.
The size of the clearance between the inner and outer surfaces 207 and 209 influences to an amount of heat transmitted between those by the laser. Should the clearance be too wide, welding will be insufficient due to the low amount of the transmitted heat. No hermeticity is obtained because no firm attachment is obtained between the receiving opening 205 and the plug head 206. Furthermore, the sealed terminal device 200 may be dropped away from the hermetic shell 201 by damage of the weld area. Should the clearance be too narrow, welding will be excessive due to the high amount of the transmitted heat. Hermeticity is lost because the sealed terminal device 200 is overmelted to break the insulating encapsulant 203 in the outer ring 202. It is necessary in the laser welding to regularize the size of the clearance between the inner and outer surfaces, 207 and 209 to regulate an amount of the transmitted heat of laser from the inner surface 207 to the outer surface 209.
In FIGS. 9A and 9B, the inner and outer surfaces 207 and 209 of the receiving opening 205 and the plug head 206 are directed in the axial direction of the plug head 206. It is necessary to increase precision of an outer diameter Φ1 of the outer surface 209 and an inner diameter Φ2 of the inner surface 207 for regularizing the size of the clearance between the inner and outer surfaces 207 and 209. However, the sizes of the sealed terminal device 200 and the hermetic shell 201 are as small as several millimeters, because of an outer diameter of 3 mm or so. It is very difficult to obtain the outer diameter Φ1 of the outer surface 209 and the inner diameter Φ2 of the inner surface 207 at a high precision. The size of the clearance between the inner and outer surfaces 207 and 209 cannot be easily regularized. Possibility of ensuring hermeticity of the hermetic shell 201 with the sealed terminal device 200 is low, to decrease the yield of the product.